Transit time tube having extremely low phase distortion

ABSTRACT

A transit time tube having a delay line which is arranged between an electron beam generating system and an electron collector, and which contains sections exhibiting different degrees of delay, employs at least one section of the delay line, a phase distortion correction section, which possesses a degree of delay which is reduced relative to the degree of delay of the section at the electron beam generating end.

United States Patent [1 1 Heynisch et al.

[ TRANSIT TIME TUBE HAVING EXTREMELY LOW PHASE DISTORTION [75] Inventors: Hinrich IIeynisch, Gracfelt'mg;

Klaus Poeschl, Furth; Werner Veith, Munich, all of Germany [73] Assignee: Siemens Aktiengesellschaft, Berlin & Munich, Germany 22 Filed: Aug. 2, 1973 211 Appl. No.: 385,158

[30] Foreign Application Priority Data Aug. 10, 1972 Germany 2239459 [52] US. Cl. 315/3.6, 315/393 [51] Int. Cl. IIOlj 25/34 [58] Field of Search 315/3.6, 39.3

[56] References Cited UNITED STATES PATENTS 2,908,844 l0/l959 Ouate SIS/3.6

[ Jan. 28, 1975 2,922,920 1/1960 Convert 315/31) 2,948,828 8/l960 Ashkin 315/31 3,092,750 6/1963 Haus et al 3I5/3.6 3,614,517 lO/l97l Dionne INS/3.6 3.76L760 9/l973 Harper 315/31 Primary Examiner-Archie R. Borchelt Assistant ExaminerSaxfield Chatmon, Jr.

Attorney, Agent, or Firm-Hill, Gross. Simpson, Van Santen, Steadman, Chiara & Simpson [57] ABSTRACT A transit time tube having a delay line which is arranged between an electron beam generating system and an electron collector, and which contains sections exhibiting different degrees of delay, employs at least one section of the delay line, a phase distortion correction section, which possesses a degree of delay which is reduced relative to the degree of delay of the section at the electron beam generating end.

9 Claims, 4 Drawing Figures TRANSIT TIME TUBE HAVING EXTREMELY LOW PHASE DISTORTION BACKGROUND OF THE INVENTION 1-. Field of the Invention This invention relates to a transit time tube having a delay line which is arranged between an electron beam generating system and an electron collector, and which contains sections exhibiting different degrees of delay.

2. Description of the Prior Art If the transmission of active power, i.e. the amplification in a transit time tube is not determined by linear processes, the displacement of the output phase relative to the input phase of an amplified wave will become dependent upon amplitude and frequency as is well known and phase distortions result in the signal which is to be transmitted. Signal adulterations of this type are particularly disturbing, for example, when the transit time tube is employed for radio relay purposes, in which case the signal transmission is effected by means of frequency modulation. A gauge for the phase distortion is the so-called amplitude modulation/phase modulation conversion factor (AM/PM conversion factor); in particular in the case of radio relay traveling wave tubes, a maximum value of clearly below 2/dB is desirable for this factor, in order to keep the expense for amplitude limitation within reasonable limits.

In order to reduce the conversion factor, it has become known in the art, for example from the German patent application 1,491,383, in a transit time tube having a helix-shaped delay line partially provided with attenuating material, to maintain the attenuation constant with respect to each length unit-except for necessary taperings. The attenuation free output end of the delay line is to be at least ten wave lengths long over the entire operating wave length range of the arrangement, and the value of the product QC (space charge parameter) for the tube is to amount to at least 0.4. An arrangement of this kind exploits the distortion compensating influence of relatively strong space charge fields, and is therefore simultaneously limited to transit time tubes with high perveance and with specific dimensioning rules for the delay line.

SUMMARY OF THE INVENTION The object of the present invention is to provide a transit time tube with an extremely low phase distortion which is substantially independent of drive, which is considerably free of the above mentioned limitations in the tube parameters.

For the realization of the above object it is proposed, in accordance with the invention, that in transit time tubes of the type mentioned above, at least one section of the delay line be provided with a degree of delay which is reduced in relation to the degree of delay of the section arranged at the electron beam generating end.

The invention is based on the recognition that the phase distortion correction is influenced not only by the magnitude of the space charge, but also by a change in the degree of delay, in the course of the delay line, and that this change also be in fact used for the correction of the phase distortion. It has been discovered that when a section having a reduced degree of delay is connected into the delay line, the phase of the wave in the beam can be displaced relative to the phase of the wave on the line in a distortion compensating fashion over a large drive range. The exact amount of the reduction in the degree of delay which is carried out for the section of the line must be in accordance with the size of the predetermined space charge parameter QC on the one hand and the line dimensioning and attenuation factors on the other hand. However, these parameter values may be selected freely. This freedome which has been achieved in respect of the design of the transit time tube means that it is possible to carry out the compensation of the phase distortion proposed by the present invention as a subsequent step in already existing tube concepts.

The change, proposed in accordance with the invention, in the average degree of delay might first appear to be inapt, since it is well known that the degree of delay along a delay line has previously fundamentally only been modified in order to improve the efficiency of the tube by matching the wave speed to the electrons which are decelerated as a result of the energy output. In a speed tapering process of this kind, it is necessary to gradually increase, not reduce, the degree of delay at the output end of the delay line. Actually, the measure in accordance with the present invention causes the efficiency to be somewhat reduced in comparison to a tube having an untapered delay line. In many cases, however, it is possible to accept this loss, or to compensate it by lengthening the reaction section or reducing the electron collector potential.

In a further development of this invention, it is pro posed that the phase distortion correction section be followed at the electron collector end by a section having a degree of delay which is increased, in a known manner, in relation to the degree of delay of the section at the electron beam generating end. It has been proven that as a result of this additional measure the aforementioned loss of efficiency can be fundamentally absorbed, while at the same time preserving the phase distortion correcting capacity.

BRIEF DESCRIPTION OF THE DRAWING Other objects, features and advantages of the invention, its organization, construction and operation will be best understood from the following detailed description taken in conjunction with the accompanying drawing, on which:

FIG. 1 is a schematic representation of a transit time tube constructed in accordance with the present invention;

FIGS. 2 and 3 are diagrams of examples of delay degree changes within the scope of the invention; and

FIG. 4 is a diagram of the dependence of the AM/PM conversion factor along the drive power.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The schematic illustration in FIG. 1 shows a transit time tube constructed in accordance with the invention in the form of a traveling wave tube having a coiled line. The tube comprises an electron beam generating system 1 and an electron beam collector 2, between which is arranged the coil 3. A pair of arrows 20 and 21 indicate the high frequency input coupling and output coupling of the delay line. The coil 3 is divided into an input section 5 and an output section 6 by an attenuating link 4 which is shown shaded and, in its triangular form is to represent the conventional tapering.

The change in the degree of delay which is proposed in accordance wih the invention is, in this case, effected in such a manner that the phase distortion correcting section followsthe electron beam generating end section in the region of the attenuating link 4, and in fact at the point of its extreme maximum attenuating force (the point 8). In the case of an untapered attenuating length it is advantageous to arrange the structure so that the phase distortion correcting section begins at the end of the attenuating link facing the electron collector 2. In this case, the reduction in the degree of delay is effected by increasing the coil pitch 7. In practice, it is preferred that the individual sections blend into one another with constant changes in degree of delay, in order to avoid discontinuities.

In the case of the transit time tube illustrated in FIG. 1 it is advisable to observe the following and easily kept limiting conditions in order to omtimize the phase distortion correction and the efficiency; 0.8 'y 2.0 should apply, in which y is the amplification parameter of the electromagnetic wave; furthermore, the amplification gain at the output part 6 of the delay line should amount to a minimum of 24 dB; furthermore, d 0.1 should apply wherein dis a gauge for the inherent losses of the delay line in the output section (d =-a,,/- B,.C wherein 01,, is the attenuation constant of the system, [3,. is the phase constant of the electron flow and C is the amplification parameter); and finally, 2 A 1,, 6A,, should apply, wherein I is the length of the attenuation link and is the length of the electromagnetic wave in the reaction section. The exact dimensioning of the course of the delay line will then, for a specific line type, depend not only upon the selected space charge parameter, but also upon these freely selectable tube parameters, and can be calculated or experimentally determined.

The diagrams in FIGS. 2 and 3 illustrate examples for degrees of delay along a delay line in transit time tubes in accordance with the invention. Here, the degree of delay, defined as the ratio of the speed of light 0 to the phase speed v ofthe wave in the delay is plotted against the length coordinate L of the delay line. Whereas FIG. 2 illustrates examples with an untapered input section 5, FIG. 3 represents tapered input sections 5 in which case the proposed delay degree relations must apply to the average degrees of delay of both sections. Examples of the change in degree of delay in accordance with the invention, as illustrated by the curves ll, l2, 13, 14 and 15, have been provided in comparison to a constant degree of delay shown by the curve 10. All of the changes move within the 10 percent limits.

FIG. 4 illustrates the effect of a change in degree of delay in accordance with the invention on the phase distortion. In a diagram the AM/PM coefficient k, is plotted against the drive power, shown in relative units A. Here the curve 100 corresponds to the delay line with a constant degree of delay (curve 10 in FIG. 2), and the curve 110 corresponds to the same delay line, but with a design in accordance with the invention corresponding to the curve 11 in FIG. 2. This comparison was carried out with a helix line as indicated in FIG. 1. The considerable reduction in the conversion factor which is achieved by the measure of practicing the present invention is illustrated, which, in the exemplary embodiment corresponding to the curve 110 achieves a maximum value of only approximately l/dB and therefore constantly remains clearly under Z I dB. as required.

The present invention is, of course, not restricted to the particular type ofembodiment of a transit time tube and neither to a traveling wave tube, nor to a specific type of delay line. Furthermore, the proposed change in degree of delay can be effected not only by a period variation of the delay line but also by other measures such as, for example, changes in cross section of the delay line or by the introduction of the dielectric material.

Many other changes and modifications of the invention-may become apparant to those skilled in the art without departing from the spirit and scope of the invention. We therefore intend to include within the patent warranted hereon all such changes and modifications as may reasonably and properly be included within the scope of our contribution to the art.

We claim:

1. A transit time tube comprising: an electron beam generating system; an electron collector; and a delay line extending between said beam generating system and said collector including a plurality of delay sections, at least one of said sections being a phase distortion correction system and having a degree of delay which is less than the degree of delay of the section at the beam generating end. and a section following and distortion correcting section at the electron collector end and having a degree of delay which is greater than the degree of delay of the section at the electron beam generating end, said delay line including an attenuation link, said correcting section following said attenuation link.

2. The invention of claim I, wherein the relation 0.8 a y a 2.0 holds true, where y is the amplification constant for the electromagnetic wave.

3. The invention of claim I, wherein said delay line sections are constructed so that the degrees of delay of the individual sections blend smoothly into one another.

4. The invention of claim 1, wherein said delay line comprises a helix-shaped coil of varying coil pitch and the different degrees of delay are defined by the pitches of the coil.

5. The invention of claim I. wherein said delay line includes a section following said attenuating link and having a degree of amplification of at least 24 dB.

6. The invention of claim I, wherein the relation d -a,,/B,,C holds true, where d 0.1, a is the attenuation constant for the electromagnetic wave, B is the phase constant of the electron flow and C is the amplification parameter.

7. The invention of claim I, wherein the relation 2 l, 6A,, holds true where is the length of said attenuating link and k,, is the wave length of the electromagnetic wave in the reaction section.

8. The invention defined in claim 1, wherein said attenuation link has a maximum attenuating force between two tapering attenuating forces. said correcting delay section having a degree of amplification of at least 24 dB and begins at the point of maximum attenuating force, the relations 0.8 s y, s 2.0. d 0.1 d -a,,/B,.C and 2A l 6A holds true where 7,, 15 the amplification constant for the electromagnetic wave. a, is the attenuation constant for the electromagnetic wave, [3,. is the phase constant of the electron flow. C is the amplification parameter, 1,, is the length of the atdistortion correction section at the electron collector end and having a degree of delay which is greater than the degree of delay of the section at the electron beam generating end, and an attenuating link; said distortion correcting section following said attenuating link, said attenuating link having a maximum attenuating force between a pair of tapering attenuation forces, said correcting section beginning at the point of maximum at- 

1. A transit time tube comprising: an electron beam generating system; an electron collector; and a delay line extending between said beam generating system and said collector including a plurality of delay sections, at least one of said sections being a phase distortion correction system and having a degree of delay which is less than the degree of delay of the section at the beam generating end, and a section following said distortion correcting section at the electron collector end and having a degree of delay which is greater than the degree of delay of the section at the electron beam generating end, said delay line including an attenuation link, said correcting section following said attenuation link.
 2. The invention of claim 1, wherein the relation 0.8 > or = gamma a > or = 2.0 holds true, where gamma a is the amplification constant for the electromagnetic wave.
 3. The invention of claim 1, wherein said delay line sections are constructed so that the degrees of delay of the individual sections blend smoothly into one another.
 4. The invention of claim 1, wherein said delay line comprises a helix-shaped coil of varying coil pitch and the different degrees of delay are defined by the pitches of the coil.
 5. The invention of claim 1, wherein said delay line includes a section following said attenuating link and having a degree of amplification of at least 24 dB.
 6. The invention of claim 1, wherein the relation d - Alpha o/ Beta eC holds true, where d < 0.1, Alpha o is the attenuation constant for the electromagnetic wave, Beta e is the phase constant of the electron flow and C is the amplification parameter.
 7. The invention of claim 1, wherein the relation 2 lambda w < lD < 6 lambda w holds true where lD is the length of said attenuating link and lambda w is the wave length of the electromagnetic wave in the reaction section.
 8. The invention defined in claim 1, wherein said attenuation link has a maximum attenuating force between two tapering attenuating forces, said correcting delay section having a degree of amplification of at least 24 dB and begins at the point of maximum attenuating force, the relations 0.8 < or = gamma a < or = 2.0, d < 0.1 d - Alpha o/ Beta eC and 2 lambda w<lD<6 lambda w holds true where gamma a is the amplification constant for the electromagnetic wave, Alpha o is the attenuation constant for the electromagnetic wave, Beta e is the phase constant of the electron flow, C is the amplification parameter, lD is the length of the attenuating link and lambda w is the length of the electromagnetic wave in the reaction section.
 9. A transit time tube comprising: an electron beam generating system; an electron collector; and a delay line extending between said beam generating system and said collector including a plurality of delay sections, at least one of said sections being a phase distortion correction section and having a degree of delay which is less than the degree of delay of the section at the beam generating end, and a section following said distortion correction section at the electron collector end and having a degree of delay which is greater than the degree of delay of the section at the electron beam generating end, and an attenuating link, said distortion correcting section following said attenuating link, said attenuating link having a maximum attenuating force between a pair of tApering attenuation forces, said correcting section beginning at the point of maximum attenuating force. 